The featured paper is ‘Cognitive Impairment and Functional Outcome after Stroke Associated with Small Vessel Disease’ by Mok et al and is freely available here.
The authors of have clearly identified aims for this study which looks at the relationship between small vessel disease associated stroke and cognitive impairment. They are interested in characterising the nature of this cognitive impairment, the causes and the relationship with functional outcome.
In order to assess these outcomes the researchers include consecutive admissions to a stroke unit in Hong Kong and also specify very strict inclusion criteria in terms of identified lesions on CT and MRI. Nevertheless it can be argued that there are certain groups that might be excluded. Thus people that might not be included in this group would be those with ‘silent’ infarcts, those who would have a high threshold for utilising services and those who have events occurring in the context of marked cognitive impairment. Since intracerebral haemmorhage is being excluded, the sample consists of people with clinically apparent small vessel disease sufficient for recognition in the community and subsequent referral to hospital. The researchers include an extensive list of other exclusion criteria which includes depression as well as probable cardiac emboli and carotid artery stenosis. Thus the sample population in the study is not representative of the general population or of those with small vessel disease. I think the reason for these very tight criteria is to try as far as possible to select people with ‘pure’ and well demarcated subcortical lesions which may allow greater confidence in drawing relationships with ‘corresponding’ cognitive impairment.
The researchers use a number of cognitive measures that have been translated into chinese and validated. Functional outcomes were also assessed using the Barthel Index and Lawton IADL. An ANCOVA was used to compare controls and subjects on psychological measures. When the subjects were divided into three groups, the researchers used a Mann-Whitney U test with a Bonferrini correction (the correction should reduce the likelihood of false positive results).
Of 294 consecutive patients admitted to the stroke unit, 86 patients remained. Cognitive problems including bradyphrenia were reported by patients although self-reporting might not be sensitive to some of the subtle cognitive difficulties that may arise. CDR>=1 was significantly associated with impaired IADL and psychometric performance. Previous stroke and cognitive decline prior to the current episode (using pre-stroke IQCODE) were significantly associated with severity of cognitive impairment although the latter in particular may have many causes and may well support an interaction between such processes (there has been recent evidence in this regards of an interaction between vascular lesions and Alzheimer’s Disease pathology). In this patient sample, the researchers found that executive dysfunction was significantly associated with ‘complex ADL’. As this is a longitudinal study (because patients were identified at the time of stroke and assessed three months later), the authors refer to predictions rather than associations in a number of cases. They also draw a number of cautions given the sample size in certain cases.
In conclusion, in my opinion, this is an excellent paper. The researchers have clearly defined aims, have used validated instruments, produced unambiguous exclusion criteria, employed a longitudinal design, specified the statistical analysis including corrections for multiple comparisons, reported results clearly and in the discussion have identified shortcomings in the study and systematically addressed the aims.
Steps to Treatment = 4 (replication, incorporation into diagnostic criteria, incorporation into policy, use in practice followed by treatment).
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